Elaboration
By contact sound we mean sounds which enter the home from other homes and buildings by way of communal constructions, mainly walls, ceilings and floors. Sound consists of a wave and a frequency and enters the ear when the air vibrates. Contact sound is from a source (e.g. music, machines, slamming doors) which makes the construction vibrate, which in turn makes the air vibrate. The construction functions as a sounding board and increases the noise level at the other side of the structure.
The transmission of sound doesn’t only depend on the construction of the partition, but also on the character of the construction and the fit of various parts (cracks and seams). As the mass increases, so does the sound insolation. Concrete, stone and wood have a relatively high mass which blocks much of the sounds. Lighter constructions will resonate more readily in frequencies which are audible to the human ear. (Derived from Eerens & Baars.)

In the (exceptional) case one has a home built with an autistic child in mind, noise should be a prime concern.
Structural measures against noise in new buildings is the competence of the architect. The measures he or she takes depend on the local situation, while every day new techniques to this end become available. For these reasons our recommendations are modest and should be taken as no more than suggestions.
These suggestions are to lessen noise transmitted through walls and floors by:

adding a floating top floor

place a felt band on the foundation wall on which the floor rests

using coreless cavity walls with sound-insulating padding

avoid wall anchors as much as possible; these are formidable sound bridges.

Of autistic people in general and children in particular it is known that they don’t only suffer from the loudness of sounds, but also when they come suddenly; besides they are often confused by their origin. From their perspective it doesn’t matter much from where the noise comes. While here we distinguish between contact noise in the home, reverberation (recommendation 76), sounds from other residents or from outside, the child doesn’t because it has difficulty interpreting its nature. This is probably another manifestation of weak Central coherence by which one’s attention is drawn to details separated from their context. Since none of these sound sources can be silenced completely, an important parental task is explaining the origin and nature of sounds, which may considerably reduce the confusion caused by them.